The present invention relates to a liquid crystal display device member for backlit lighting devices, liquid crystal display devices utilizing that member and also liquid crystal display device manufacturing technology.
In recent years compact, low priced and low current consumption portable information terminals and cellular telephones have come into widespread use. Display devices for this equipment normally use a transreflective liquid crystal display device for both good screen (image visibility) recognition when outdoors in daylight and good screen (image visibility) recognition in dark locations. Along with the trend towards portable information terminals and cellular telephones having color screens and moving images, the need has arisen for backlit light source devices having high brightness but no dark spots and that light the entire flat surface of the screen.
FIG. 2 shows a backlit lighting device of the related art having compact liquid crystal display elements for use in portable information terminals and cellular telephones.
A perspective view of the backlit lighting device of the related art is shown in FIG. 2. As shown in the figure, light emitting diodes are mainly used as the light source 1 in view of the need to limit power consumption and save mounting space. These (LED) are installed on the edge of a light guide plate 2 made of transmittant material, and a reflective plate 4 for reflecting light and dots 3 for reflecting, transmitting and scattering light on the upper and lower surfaces of the light guide plate, and a diffuser plate 5 made from opaque synthetic plastic having a light scattering effect for evenly distributing the lighting surface brightness on the upper surface of light guide plate 2 over the entire surface are installed. Further, a first prism sheet 6 and a second prism sheet 7 are installed on that upper surface to concentrate the diffused light to some extent, and improve the brightness on the front side of the display device. The reference numeral 9 in the figure is the light emitted from the light source 1. A light/dark section is present near the position where the light source 1 for the light guide plate 2 is installed and is therefore masked by a frame (not shown in drawing).
However, the light emitting diodes constituting the light source 1 were a point light source, causing the problem that dark spots appeared near the display surface of the light source 1 degrading the display quality. Measures to reduce these dark spots on the light emitting diodes of light source 1 were to increase the number of light emitting diodes, and to lengthen the distance between the display surface and the light source 1. However, these measures had the problem that if the number of light source 1 were increased then power consumption became larger and the cost is increased. If the distance the display surface and the light source 1 is increased then the available display area is diminished.
Methods were also disclosed in the related art in Japanese Unexamined Patent Publication No. 259623/1999, Japanese Unexamined Patent Publication No. 2001-110224, and Japanese Unexamined Patent Publication No. 2001-135121, to resolve the above mentioned problems by contriving a shape for the light guide input section of the light guide plate to reduce the dark spots. However, these methods had the problems that the light emitting diode and light guide plate required installation precision, a drop in brightness occurred due to the light spreading out from the light guide input section, the display area became narrow, there was less freedom in design of the backlight, optical (system) design was difficult, and mold manufacturing was difficult, etc.
A method on the other hand using a light guide element for changing the point light source into a line light source was disclosed in Japanese Unexamined Patent Publication No. 249759/1999. However, the light guide element has poor efficiency for turning the point light source into a line light source and the further problems that there was a drop in brightness, an increased number of parts were needed and the cost became high.
A technology of the related art was also disclosed in Japanese Unexamined Patent Publication No. 254618/1996 for decreasing the number of dark spots by forming a prism on the light guide input surface of the light guide plate. However, this method had many problems, namely that the brightness lines generated from the light source were not effective enough in preventing dark spots, manufacturing the mold for forming the prism on the light input surface was difficult, and further not all the light was reflected during reflection at the oblique surface portion and much of the light returning to the light source had low brightness.
A method of the related art for reducing dark spots by contriving a shape for the side surface of the light guide plate was also disclosed in Japanese Unexamined Patent Publication No. Hei 2000-299012. However, this method also had problems such as that optical (system) design was difficult, there was little freedom in the backlight design, and mold manufacture was difficult, etc.
The methods of the related art were therefore able to reduce the dark spots but also drawbacks due to the various problems that arose and eliminating these problems was impossible.
The present invention therefore has the object of resolving the problems of the related art by providing a backlit lighting technology capable of reducing dark spots. In order to achieve the above objects, the liquid crystal display device of the present invention is comprised of a backlit lighting device containing a light guide plate, a light source installed on the side surface of the light guide plate, and light directional diffusing elements formed on either the upper surface or lower surface of the light guide plate near the light source and, a liquid crystal element, wherein the light emitted from the backlit lighting device is irradiated onto the liquid crystal element.
The light directional diffusing elements are hologram elements, diffraction gratings, cylindrical lenses array or microlens arrays.
In the case of hologram elements, the height of the elements is 3 to 30 micrometers, and the element height divided by the element gap is at least 0.15. In the case of diffraction gratings, the height of the diffraction gratings is 3 to 30 micrometers, and the diffraction grating height divided by the grating gap is at least 0.15. In the case of the cylindrical lens array, the height of the lens is 3 to 30 micrometers, and the lens height divided by the grating gap is at least 0.15, the shape of the lens cross section is a portion of an ellipse, and the length of the flat section of the lens is 2 to 10 micrometers. In the case of the microlens array, the microlens flat surface shape is circular, elliptical, hexagonal, quadrangular or square with rounded edges, and that lens height is 3 to 30 micrometers, and the lens height divided by the lens gap is at least 0.15.
Further, a plurality of microdots made from a plurality of small protrusions or small depressions are formed on the upper surface or on the lower surface on the light guide plate near the light source, to change the light progression direction that the plane light is emitted from the light source, and the hologram element height or diffraction grating height or lens height of the cylindrical lens are essentially the same as the height (depth).
The flat surface of the microdot may be elliptical or a square with rounded edges with a length (long side) of 20 to 100 micrometers, and a value from 1 through 5 for long side divided by short side, and a dot cross sectional shape that is a portion of an ellipse, and a dot height of 3 to 30 micrometers. Further, the number of dots, and/or shape and/or size may be changed as needed to achieve a uniform brightness distribution.
These and other objects, features and advantages of the invention will become apparent from the following more particular description of the preferred embodiments of the invention as illustrated in the accompanying drawings.